Typical construction of an oil or gas well includes the operations of assembling a casing string, inserting the casing string into a wellbore, and cementing the casing in place in the wellbore. Casing assembly involves connecting multiple individual lengths of pipe (or “joints”) to form an elongate casing string. Threaded connections are usually used to join the individual lengths of pipe, requiring the application of torque to “make up” the connections, or to “break out” the connections should the string need to be disassembled. After a wellbore has been drilled to a desired depth into a subsurface formation, by means of a rotating drill bit mounted to the end of a drill string, the drill string is withdrawn and the casing string is then inserted essentially coaxially within the wellbore.
In the alternative method known as casing drilling (or “drilling with casing”), the wellbore is drilled with a drill bit mounted to the bottom of the casing string, eliminating the need for a separate drill string. After the well is drilled, the casing remains in the wellbore. As used in this patent document, the term “drill string” is to be understood, in the context of the drilling phase, as referring to the casing string for purposes of well construction operations using casing drilling methods.
During the drilling phase of well construction, a selected drilling fluid (commonly called “drilling mud”) is pumped under pressure downward from the surface through the drill string, out through ports in the drill bit into the wellbore, and then upward back to the surface through the annular space that forms between the drill string and the wellbore (due to the fact that the drill bit diameter is larger than the drill string diameter). The drilling fluid, which may be water-based or oil-based, carries wellbore cuttings to the surface, and can serve other beneficial functions including drill bit cooling, and formation of a protective cake to stabilize and seal the wellbore wall.
Once the well has been drilled to a desired depth and the casing is in place within the wellbore, the casing is cemented into place by introducing a cement slurry (commonly referred to simply as “cement”) into the wellbore annulus. This is typically done by introducing an appropriate volume of cement into the casing string (i.e., a volume corresponding to the volume of the wellbore annulus), and then introducing a second and lighter fluid (such as drilling mud or water) into the casing under pressure, such that the second fluid will displace the cement downward and force it out and around the bottom of the casing, and up into the wellbore annulus. In the typical case, this operation is continued until the cement has risen within the wellbore annulus up to the top of the casing. Once thus cemented, the casing acts to structurally line the wellbore and provide hydraulic isolation of formation fluids from each other and from wellbore fluids.
In some applications it is desirable to introduce cement into the casing through a tubular “inner string” inserted into the casing bore and arranged to extend from the proximal (i.e., upper) end of the casing string to a selected depth, typically near the distal (i.e., lower) end of the casing string or near what is referred to as the “casing shoe”. The inner annulus between the inner string and casing is left fluid-filled and sealed near the proximal end of the casing so that cement pumped through the inner string is then introduced into the casing near the shoe. The fluid filling the inner annulus tends to prevent cement flow up the inside of the casing and instead the cement is urged to immediately enter the casing wellbore annulus during pumping. This is known in the art as an “inner string cement job” and typically requires an adaptor nubbin, sealingly connecting between the casing and the inner string. On top-drive-equipped rigs, the adaptor nubbin also connects to the top drive, facilitating the functions of rotation and reciprocation during cementing to further promote distribution of the cement in the casing to the wellbore annulus.
It is increasingly common in the drilling industry to use top-drive-equipped drilling rigs instead of traditional rotary table rigs, and to install casing (an operation commonly referred to as “casing running”) and/or to drill with casing directly using the top drive. Casing running tools (CRTs), such as the “Gripping Tool” described in U.S. Pat. No. 7,909,120, connect to the top drive quill and support these well construction operations by engaging the upper end of the tubular string (i.e., drill string or casing string, as the case may be) so as to allow transfer of axial and torsional loads between the tubular string and the top drive, and to allow the flow of fluids (such as drilling mud and cement) into or out of the casing string through a central passage or bore in the tool. Such tools thus enable the top drive to be used for make-up and break-out of connections between joints of pipe, hoisting and rotation of tubular strings, casing fill-up, circulation of drilling mud, and cementing of casing.